Problem: A right triangle has a side length of 21 inches and a hypotenuse of 29 inches. A second triangle is similar to the first and has a hypotenuse of 87 inches. What is the length of the shortest side of the second triangle?
Explanation: Using the Pythagorean Theorem, we calculate that the other leg of the original right triangle must be $$\sqrt{29^2 - 21^2} = \sqrt{841 - 441} = \sqrt{400} = 20$$ inches. Since 87 is 3 times 29, the length of the shortest side of the second triangle must be $3 \times 20 = \boxed{60\text{ inches}}$.